Synthesis, crystal structures, reactivity, and magnetochemistry of a series of binuclear complexes of manganese(II), -(III), and -(IV) of biological relevance. The crystal structure of [L'MnIV(.mu.-O)3MnIVL'](PF6)2.H2O containing an unprecedented short Mn.cntdot..cntdot..cntdot.Mn distance of 2.296 .ANG.